The disclosure relates generally to gas turbine engines, and, more specifically, to micro-channel cooling therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in a high pressure turbine (HPT), which powers the compressor, and in a low pressure turbine (LPT), which powers a fan in a turbofan aircraft engine application, or powers an external shaft for marine and industrial applications.
Engine efficiency increases with temperature of combustion gases. However, the combustion gases heat the various components along their flowpath, which in turn requires cooling thereof to achieve an acceptably long engine lifetime. Typically, the hot gas path components are cooled by bleeding air from the compressor. This cooling process reduces engine efficiency, as the bled air is not used in the combustion process.
Gas turbine engine cooling art is mature and includes numerous patents for various aspects of cooling circuits and features in the various hot gas path components. For example, the combustor includes radially outer and inner liners, which require cooling during operation. Turbine nozzles include hollow vanes supported between outer and inner bands, which also require cooling. Turbine rotor blades are hollow and typically include cooling circuits therein, with the blades being surrounded by turbine shrouds, which also require cooling. The hot combustion gases are discharged through an exhaust which may also be lined and suitably cooled.
In all of these exemplary gas turbine engine components, thin walls of high strength superalloy metals are typically used to reduce component weight and minimize the need for cooling thereof. Various cooling circuits and features are tailored for these individual components in their corresponding environments in the engine. For example, a series of internal cooling passages, or serpentines, may be formed in a hot gas path component. A cooling fluid may be provided to the serpentines from a plenum, and the cooling fluid may flow through the passages, cooling the hot gas path component substrate and any associated coatings. However, this cooling strategy typically results in comparatively inefficient heat transfer and non-uniform component temperature profiles.
Employing micro-channel cooling techniques has the potential to significantly reduce cooling requirements. Micro-channel cooling places the cooling as close as possible to the heat flux source, thus reducing the temperature difference between the hot side and cold side of the load bearing substrate material for a given heat transfer rate. However, current techniques provide for the forming of one or more grooves within a substrate layer with a subsequent application of one or more coating layers to bridge the one or more grooves and define the micro-channels. In many instances, forming the microchannels typically requires specialized techniques, such as, the use of sacrificial fillers, re-entrant grooves, angular deposition techniques, or the like. The use of sacrificial fillers keeps the coating from being deposited within the microchannels while supporting the coating during deposition. Subsequent to deposition of the coating system, the sacrificial filler (fugitive) material is removed. The filling of the channels with a fugitive material, and the later removal of that material presents potential problems for current micro-channel processing techniques. Removal of the sacrificial filler involves potentially damaging processes of leaching etching, or vaporization and typically requires long times. Residual filler material is also a concern. Other micro-channel coating deposition techniques include the fabrication of re-entrant grooves, in which a groove opening at the surface is small enough that the coating particles form a bridge with little or no deposition being deposited inside the groove, and thus within the formed micro-channel. In addition, angular deposition techniques have been utilized for the coating deposition thereby decreasing the line-of-sight into the channel opening. These techniques while providing for the deposition of the coating layer may require complex machining techniques, strict tolerances, and may inadvertently allow unwanted coating particles to be deposited into the micro-channels or channel openings.
It would therefore be desirable to provide a method for forming cooling channels in hot gas path components that provide for reduced fabrication time and techniques.